The present invention relates generally to inkjet printheads, and more particularly to reducing data bandwidth to inkjet printheads.
A conventional inkjet printing system includes a printhead, an ink supply which supplies liquid ink to the printhead, and an electronic controller which controls the printhead. The printhead ejects ink drops through a plurality of orifices or nozzles and toward a print medium, such as a sheet of paper, so as to print onto the print medium. Typically, the orifices are arranged in one or more arrays such that properly sequenced ejection of ink from the orifices causes characters or other images to be printed upon the print medium as the printhead and the print medium are moved relative to each other.
Typically, the printhead ejects the ink drops through the nozzles by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as thin film resisters. Heating the ink causes the ink to vaporize and be ejected from the nozzles. Typically, for one dot of ink, a remote printhead or electronic controller typically located as part of the processing electronics of a printer, controls activation of an electrical current from a power supply external to the printhead. The electrical current is passed through a selected thin film resister to heat the ink in a corresponding selected vaporization chamber.
Advanced printhead designs now permit an increased number of nozzles to be implemented on a single printhead. As the number of nozzles increases, an overall number of ink drops which can be ejected per second is increased. Since the overall number of drops which can be ejected per second is increased, printing speed can be increased as long as the data rate or bandwidth to the printhead is correspondingly increased.
As the number of nozzles on a single printhead increases, the number of corresponding thin film resisters which need to be electrically coupled to the remote printhead controller correspondingly increases, which results in a correspondingly large number of conductive paths carrying nozzle data and other data signals to the printheads in order to maintain sufficient bandwidth to the printhead. Furthermore, the number of drivers in the electronic controller necessary to transmit the nozzle data and other data signals from the electronic controller to the printhead is also increased to maintain sufficient bandwidth to the printhead. In addition, a corresponding increased number of input pads are required on the printhead to receive the nozzle data and other data signals at the increased bandwidth.
Voltage switching in the large number of signals carried on the conductive paths required for sufficient bandwidth generates undesirable electromagnetic interference (EMI). In addition, the ejection of ink from the nozzles (i.e., firing of the nozzles) requires a switching on and off of a large amount of electrical current in a short amount of time. The switching on and off of nozzle current of a large number of nozzles simultaneously generates undesirable EMI.
The EMI generated as a result of voltage switching in the signals carried on the conductive paths and nozzle firing causes conductive paths, such as cables, to conduct and/or radiate undesirable EMI. EMI is undesirable because EMI interferes with internal components of the printing system and can also interfere with other electric devices and appliances not associated with the printing system, such as computers, radios, and televisions. Moreover, systems, such as printing systems, typically need to comply to an electromagnetic compliance (EMC) standard which defines limits to levels of stray EMI noise signals. For example, EMC standards are set by government regulatory agencies, such as the Federal Communications Commission (FCC), which set electrical emission standards for electric devices.
Data rates or bandwidth to printheads can also be increased by increasing the speed at which the data is transmitted from the electronic controller to the printhead. Nevertheless, signal integrity of nozzle data and other data signals communicated from the electronic controller to the printhead typically degrades as the speed of the signal increases.
For reasons stated above and for other reasons presented in greater detail in the Description of the Preferred Embodiment section of the present specification, an inkjet printing system is desired which reduces bandwidth of nozzle data communicated from the electronic controller to the printhead, yet maintains desired high speed printing rates.
One aspect of the present invention provides a printhead including a first column of nozzles and a second column of nozzles. First nozzle column register and logic units are configured to receive first serial nozzle data and to provide first nozzle firing control signals for controlling the firing of ink drops from the first column of nozzles. Second nozzle column register and logic units are configured to receive the first serial nozzle data and to provide second nozzle firing control signals for controlling the firing of ink drops from the second column of nozzles. First column redundancy logic is configured to disable selected nozzles of the first column of nozzles from firing which correspond to selected nozzles of the second column of nozzles enabled for firing. Second column redundancy logic is configured to disable selected nozzles of the second column of nozzles from firing which correspond to selected nozzles of the first column of nozzles enabled for firing.
One aspect of the present invention provides a printhead assembly having at least one printhead. Each printhead includes a first column of nozzles and a second column of nozzles. First nozzle column register and logic units are configured to receive first serial nozzle data and to provide first nozzle firing control signals for controlling the firing of ink drops from the first column of nozzles. Second nozzle column register and logic units are configured to receive the first serial nozzle data and to provide second nozzle firing control signals for controlling the firing of ink drops from the second column of nozzles. First column redundancy logic is configured to disable selected nozzles of the first column of nozzles from firing which correspond to selected nozzles of the second column of nozzles enabled for firing. Second column redundancy logic is configured to disable selected nozzles of the second column of nozzles from firing which correspond to selected nozzles of the first column of nozzles enabled for firing.
One aspect of the present invention provides a method of operating a printhead including receiving first serial nozzle data with first nozzle column register and logic units, and providing first nozzle firing control signals with first nozzle column register and logic units for controlling the firing of ink drops from a first column of nozzles. The method includes receiving the first serial nozzle data with second nozzle column register and logic units, and providing second nozzle firing control signals with second nozzle column register and logic units for controlling the firing of ink drops from a second column of nozzles. The method includes disabling selected nozzles of the first column of nozzles from firing which correspond to selected nozzles of the second column of nozzles enabled for firing, and disabling selected nozzles of the second column of nozzles from firing which correspond to selected nozzles of the first column of nozzles enabled for firing.
In one embodiment of the method, the first column of nozzles includes N nozzles numbered 1 through N and the second column of nozzles includes N nozzles numbered 1 through N. In one embodiment, the disabling steps operate so that only one nozzle for a given nozzle number is enabled for firing across the first and second columns.
In one embodiment, the method includes receiving first redundant data for programming first column redundancy logic, and receiving second redundant data for programming second column redundancy logic. In one embodiment, the method includes receiving the first and second redundant data at first input pads during a configuration cycle, and receiving the nozzle data at the first input pads during a printing operation. In one embodiment, the method includes providing the first and second redundant data from the first input pads to the first and second column redundancy logic during the configuration cycle, and providing the first nozzle data from the input pads to the first and second nozzle column register and logic units during the printing operation.
In one embodiment, the method includes storing first redundancy states for the first column of nozzles, and storing second redundancy states for the second column of nozzles. In one embodiment, the method includes combining the first redundancy states with the first nozzle firing control signals, and combining the second redundancy states with the second nozzle firing control signals. In one embodiment, the combining steps are performed with AND gates.
The redundancy logic of the printhead according to the present invention permits a reduction in nozzle data rate or bandwidth by a factor of two or more for inkjet printheads that have multiple columns employed redundantly. The amount of reduced bandwidth tracks the number of columns of redundant nozzles. The significant reduction in nozzle data bandwidth to the printhead correspondingly significantly reduces the required number of conductors necessary to carry nozzle data to the printhead. The number of drivers in the electronic controller of the inkjet printing system necessary to transmit the nozzle data from the electronic controller to the printhead is also proportionally reduced. The reduction in nozzle data bandwidth to the printhead also proportionally reduces the number of required nozzle data input pads on the printhead to receive the nozzle data from the electronic controller. Moreover, the reduced number of nozzle data conductors in the electrical interconnect between the electronic controller and the printhead assembly correspondingly reduces the amount of undesirable electromagnetic interference (EMI) conducted and/or radiated by the nozzle data conductors. The reduced nozzle data bandwidth could also allow for lower speed signaling of the nozzle data transmission from the electronic controller to the printhead, which would correspondingly increase the signal integrity of the nozzle data signals communicated from the electronic controller to the printhead.